Cognitive bias assays are used as tools for evaluating the affective or emotional states of multiple species. An operant conditioning chamber, or Skinner box, is one example of an apparatus for performing cognitive bias assays on lab animals. Many cognitive bias assays, such as spatial discrimination assays, are designed for rats and often do not translate well to other species such as mice. For example, a spatial arena has been proposed that assesses a rat's cognitive bias based on the food instinct. In the spatial arena, food is placed at two different locations in the arena. At a first location, the food is accessible to the rat. At a second location, the food is trapped under a mesh such that while the food is seen and smelled by the rat, the food is inaccessible to the rat. The rat may learn not to expect food at the second location. The emotional state of the rat is assessed based on whether the rat attempts to get food at ambiguous intermediate location(s).
Some researchers have used cognitive bias assays based upon olfactory cues for rodents. For example, mice were trained with two distinct odor cues predicting either a palatable or unpalatable food treat. Subsequently, a mouse's reaction to mixtures of the odors (i.e., the ambiguous stimuli) was investigated. Variations were found in the ability of different strains of mice to distinguish between ambiguous odors, thereby weakening the ability of this test to provide meaningful and repeatable measurements of a mouse's affective state. Further, concerns exist on the ability to reliably produce appropriate olfactory cues to achieve sensitivity of assessment while avoiding odor contamination. Also, the ability to effectively eradicate all odors, including the intentional exposure odors, is problematic with animals (e.g., mice) that have highly developed levels of olfactory sensory capabilities.
As such, a physical or spatial discrimination assay is needed for distinguishing emotional affinity in lab animals. Many lab animals, such as mice for example, are burrowing creatures that prefer hidden, dark areas to open, lighted areas. Therefore, a need exists for a cognitive bias assay that is based on the burrowing tendencies of mice and other lab animals.